This invention relates to a biased trip blade apparatus for use in a moldboard assembly and, in particular, to a mechanism for controlling the biasing force acting upon the unit as it moves over an obstacle to prevent the assembly from being damaged.
Many heavy duty snow plows used to clear highways, and some smaller plows used to clear driveways and the like, are presently equipped with trip edge blades. The trip edge blade is typically hinged for rotation beneath the moldboard and is held securely in a down or operative position by means of heavy duty compression springs. The springs are held in a stationary position and are arranged to compress along the axis of the coil as the trip blade is forced back by an obstacle from the operative position toward a fully tripped, open position.
Most trip blade units presently in use cannot effectively pass over obstacles of any substantial height. Typically, the springs will become fully compressed before the blade has cleared the obstacle. As a consequence, the moldboard assembly is lifted by the obstacle. When this occurs, serious damage to both the moldboard assembly and the prime mover to which it is attached can ensue.
Torrey in U.S. Pat. No. 3,014,289 discloses a spring regulated trip blade unit wherein the trip blade is connected to a spring mechanism through means of a lost motion device. The lost motion device permits the trip blade to move back out of its operative or snow plowing position some distance before the spring is actually engaged. Although this helps to protect the blade unit from being damaged upon its striking a relatively low obstacle, it also allows the blade to swing back some distance when plowing heavy or deep snow. This results in incomplete plowing and requires multiple passes to complete the snow clearing operation.
Many curbs bordering roadways, particularly on military bases and the like, are raised to heights of ten inches or more and can be easily struck by the curb side edge of a plow. In light of the fact most trip blades extend across the entire face of the plow, this type of impact will not only tend to lift the moldboard assembly but will also produce an extremely high torque loading on the assembly.